It is known that a navigation system serves to provide position data saved in map database and promptly suggests navigational routes according to users' needs. The modern navigation systems can even be integrated into personal portable electronic tools, such as mobile phones, PDAs and so on.
Before beginning a trip for business or tourism, a user may input to a navigation system his/her destination and particular preferences for navigational route planning, such as preferences for absence of tollways or for the shortest path so that the navigation system plans a navigational route according to the request. Then the user just needs to follow the directions shown in the navigation map and voice prompts and he/she can be led to the destination through the planned route without going astray. However, in practice, during a drive many impromptu demands may be raised, such as demands for refueling or for foods or toilets, and the existing navigation systems seem imperfect in satisfying the impromptu demands during navigation.
Besides, some of the existing navigation systems rely on remote controls for operation, and thus furnish their users with only multi-level menus that are inconvenient to use and really not user-friendly. For example, FIG. 1 is a flowchart showing the operation of a conventional navigation system, which begins, as block 101, in the navigation mode of the navigation system, and the display of the navigation system displays a navigation map. When the user intends to locate a nearby gas station, he/she has to switch the navigation system into another mode to call out a main menu, as block 102, to reset the preset navigational route. Then, by a selection on the main menu, the user goes into a category menu, as block 103, to designate the category of the target facility, i.e. a gas station. Afterward, the navigation system displays a target submenu, as block 104, to provide the user with a list of nearby gas stations, typically in the order from near to far. At this time, by selecting one of the listed gas stations he/she intends to visit, the user can perform target selection, as block 105. Accordingly, the navigation system, after re-planning the navigation map, returns to the navigation mode to display the navigation map for providing the re-planned navigational route, as block 106, to direct the user to the selected gas station. This operation is complicated and time-consuming for a driver to conduct during his/her driving. Thus, if the user is just the driver himself/herself, he/she must stop the vehicle in order to conduct the operation to avoid dangerous driving. Moreover, while the conventional navigation system merely informs the user of nearby target facilities by means of a list of nearby target facilities, it is hard for the user to recognize the geographic relation between each of the target facilities in the list and the current navigational route, thus adding difficulty to the user's selection.
Although there are some other existing navigation systems using touch screens as an input interface that allows users to directly operate the touch screens and thus quickens the operation of the navigation systems, they implement the same operational steps as those depicted in FIG. 1, by which complicated setting has to be inputted through a multi-level menu.
To provide a user-friendly interface, some existing navigation systems allow users to preset exhibition of some particular categories of facilities. For instance, as shown in FIG. 2, if a user presets the navigation system to show nearby gas stations, those gas stations within a predetermined range away from the user's current location 22 can be labeled in the navigation map 20. However, such interface still fails to satisfy users' impromptu needs because it only provides a small amount of facilities located within a short distance and its operation still relies on the aforementioned multi-level menu.